Biocompatible articles including polymeric membranes having high permeability to gases and uses thereof

ABSTRACT

There is disclosed the preparation of an alpha-olefin-sulfur dioxide copolymer derived from the C8 to C18 alpha-olefins. The polymers undergo clean thermal degradation, have high permeabilities to oxygen and carbon dioxide, and are readily processed into a membrane article. Maximum permeabilities are obtained with the C16 based polymer. New uses of the copolymer are set forth including perfusion membranes, soft contact lenses and biocompatible articles for contact with human body fluids including surgical tubing, wound dressings, and prosthetic devices such as artificial veins, arteries and heart valves.

United States Patent [191 Crawford et a1.

[ BIOCOMPATIBLE ARTICLES INCLUDING POLYMERIC MEMBRANES HAVING HIGH PERMEABILITY T0 GASES AND USES THEREOF [75] Inventors: James E. Crawford, Adrian, Mich.;

Don N. Gray, Sylvania, Ohio [73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22] Filed: Feb. 2, 1973 [21] Appl. No.: 328,972

Related US. Application Data [63] Continuation-in-part of Ser. No. 279,877, Aug. 11,

1972, abandoned, which is a continuation-in-part of Ser. No. 228,240, Feb. 22, 1972, abandoned.

[52] US. Cl 260/793 A; 3/1; 3/1.4; 3/1.5; 55/16; 128/156; 128/348; l28/DIG. 24; 210/500 M; 351/160; 423/245 Dec. 23, 1975 2/1971 Moore 117/75 3,651,030 3/1972 Desaulniers 3,728,185 4/1973 Gray 156/89 OTHER PUBLICATIONS Ryden, L. L. et al., J. Am. Chem. Soc., 57, pp. 2312-2313 (1935).

Glavis, F. J. et al., J. Am. Chem. Soc. 59, pp. 707, 709 (1937).

Primary Examiner-Christopher A. Henderson, Jr. Attorney, Agent, or Firm-Richard D. Heberling; E. J. Holler [57] ABSTRACT There is disclosed the preparation of an alpha-olefinsulfur dioxide copolymer derived from the C to C alpha-olefins. The polymers undergo clean thermal degradation, have high permeabilities to oxygen and carbon dioxide, and are readily processed into a membrane article. Maximum permeabilities are obtained with the C based polymer. New uses of the copolymer are set forth including perfusion membranes, soft contact lenses and biocompatible articles for contact with human body fluids including surgical tubing, wound dressings, and prosthetic devices such as artificial veins, arteries and heart valves.

5 Claims, 12 Drawing Figures US. Patent M2119 sheet ofs 3,928,294

0 0 0. 0 w M u w Q w w W /W 0 a a 5 M m a QZfF/A/ away/u ,zz/w/z US. Patent Dec.23, 1975 Sheet5of8 3,928,294

US. Patent Dec. 23, 1975 Sheet 6 of 8 3,928,294-

5 S07 (VOA/77967 ,Zf/l/J OZ I w M5 M6 fiazyfrriz Maw/w US. Patent Dec. 2 3,1975 Sheet7of8 3,928 294 w @[4Z73 Q BIOCOMPATIBLE ARTICLES INCLUDING POLYMERIC MEMBRANES HAVING HIGH PERMEABILITY TO GASES AND USES THEREOF RELATED APPLICATIONS This is a continuation-in-part of copending US. patent application Ser. No. 279,877 filed Aug. 11, 1972 (now abandoned) which, in turn, is a continuation-inpart of copending U.S. patent application Ser. No. 228,240, filed Feb. 22, 1972 now abandoned.

This invention relates to the preparation of polymeric materials which undergo clean thermal degradation, have increased permeabilities, and are readily processable. More particularly, this invention relates to the preparation of a novel permselective membrane article consisting of an alpha-olefin-sulfur dioxide copolymer and having high biocompatibility and high permeability to gases, especially oxygen and carbon dioxide.

Copolymers from simple olefins and S have been known for some time. They were first reported by Matthews and Elder in British Pat. No. 11,635 in 1915, although the material prepared was not identified as being polymeric. Seyers and King, J. Amer. Chem. Soc. 55, 3140, in 1933 were the first to accurately describe an olefin heteropolymer of sulfur dioxide. Characterization of these compounds as high molecular weight materials was accomplished independently by Marvel and Staudinger. Reference is made to J. Amer. Chem. Soc., 56, 1915 (1934); J. Amer. Chem. Soc., 57, 1691 (1935); and Ber Bunsenges. Phys. Chem., 68,455 (1935). Both recognized that an AB-type copolymer was obtained regardless of monomer concentration, and they correctly deduced that the active polymerizing species was an olefin-sulfur dioxide complex. Marvel and Wei] later showed the polysulfone structure to be a head-to-tail configuration as evidenced from the preparation of various reference compounds that were compared with the hydrolysis products of the polymers. See J. Amer. Chem. Soc., 76, 61 (1954).

Marvel characterized a number of olefin-sulfur dioxide polymers using pyrolysis techniques. Naylor and Anderson, J. Amer. Chem. Soc., 76, 3962 (1954), prepared copolymers of ethylene, propylene, 2-butene, and isobutylene with S0 at 65-70C. using radical catalysts. They found that the propylene-sulfur dioxide polymer started to degrade at about 180C. with an activation energy of 32 kcal/mole determined from data obtained between 180 and 260C. (T for this polymer is 62.5C.). Pyrolysis of the propylene-based polymer in nitrogen at 280-290C. yielded 95.4% volatile products, with 83.4% of the initial polymer weight being monomers. Water and some unidentified sulfur-containing compounds were also isolated.

This invention is related to the preparation and properties of poly(alpha-olefin sulfones) prepared from the Series C -C3 alpha-olefins and sulfur dioxide and the use of such polymers is a permselective membrane.

Polymeric membranes having gaseous permeability are known in the prior art. Typically such membranes have comprised silicones or modified silicones. However,-the processing of such silicones is difficult. Likewise, pure polysilicone materials tend to have poor mechanical properties and may require the use of silica or other fillers. Such fillers may compromise -the ultimate performance of the polysilicone as a blood compatible bio-material.

In accordance with this invention, there is provided a polymeric material having gaseous permeability, biocompatibility, and suitable mechanical properties and which can be readily processed into a membrane article.

More especially, in accordance with this invention there is provided a novel membrane article of manufacture having high permeability, excellent nonthromobogenic properties to blood, and improved mechanical properties and consisting of a poly(alpha-olefin-sulfone) prepared from the series C to C alphaolefins and sulfur dioxide, said poly(alpha-olefin-sulfone) having the chemical structure:

l i ii l l CH dHILI cncmllcmcnls cl-icii lsi o o o where R is a straight chained, branched, or cyclic alkyl hydrocarbon radical containing six to sixteen carbon atoms.

The polymer is typically prepared via the reaction:

where [o] is any suitable catalyst such as a free radical source, light, peroxide, or azo nitrile and where R is a straight chained, branched or cyclic alkyl hydrocarbon group of six to sixteen carbons.

It is contemplated reacting a mixture of alpha-olefins with the S0 Typically the S0 and the alpha-olefin(s) are reacted in a molar ratio of 1:1.

The following represents certain experimental results and some of the best embodiments contemplated by the inventors in the practice of this invention.

MONOMER PURITY Commercial alpha olefins having a minimum monoolefin content of 98.5% (remainder being normal paraffins) were used in this study. Gas-chromatographic analysis showed less than 2% olefinic impurities consisting of other alpha-olefins.

POLYMERIZATION Bulk polymerization was used to prepare the series based on the C -C even numbered alpha-olefins and sulfur dioxide. A clean, dry nitrogen-purged citrate bottle was cooled in an ice water bath, then .liquified sulfur dioxide was added. The olefin containing 1% tert-butyl hydroperoxide, based on the olefin, was then added slowly to the citrate bottle. With an addition of a small amount of the olefin, approximately one-fourth of the total quantity, a rapid reaction occurred, resulting in a loss of some S0 After the remaining olefinperoxide mixture was added, the bottle was capped with a lined, ventable cap and the contents were allowed to warm to room temperature. Following a predetermined reaction period, usually 20 hr. at room temperature, the bottle was vented and the contents were removed. The product was kept at reduced pressure to remove the residual monomers.

MOLECULAR WEIGHTS Molecular weight (M (membrane osmometer) were all above 100,000, and some were as high as 350,000.

DIFFERENTIAL THERMAL ANALYSIS I Polymer melt temperatures were obtained using the standard capillary (micro) cell of the duPont 900 instrument, the duPont 900 with the DSC cell module, and visually using a Kofler melt bar. These data are shown in FIG. 1. All melt data were obtained on polymers having molecular weight (M,,) in excess of 150,000. It was not possible to obtain accurate glass transitions since several other second-order transformations appeared to be occurring in the temperature region where one would expect the T, to occur.

THERMOGRAVIMETRIC ANALYSIS Thermogravimetric analysis (TGA) was obtained on a duPont 900 unit in both air and nitrogen atmospheres. For screening purposes for a particular polymerization run, a heating rate of 20C./min in air with a sample size of about 10-15 mg was used. Generally the polymer decomposed cleanly. Pyrolysis started at 175C. and was essentially complete when the temperature reached 275C. One C polymer sample (M 136,000) was used to obtain kinetic data (pyrolysis) using the method of Wall and Flynn, Polymers Letters, 4, 323 (1966). TGA data were obtained at heating rates of 15 and C./min in air. The average activation energy for the pyrolytic decomposition was found to be 46-47 kcal/mole.

MASS-SPECTROMETRIC THERMAL ANALYSIS AND PYROLYSIS GAS-CHROMATROGRAPHIC ANALYSIS Mass-spectrometric thermal analysis was accomplished using the solid sample wand of the Varian M-66 mass spectrometer. The sample used was the C polymer used for the kinetic TGA runs. A wand temperature of 250C. yielded mass spectra differing only from the fragmentation pattern of the pure C -alpha-olefin by peaks at 64 and 48 mass units corresponding to the S0 and SO ion species.

For higher temperature pyrolysis studies, pyrolysis gas chromatrography was utilized. A Perkin-Elmer pyrolyzer was connected to a gas chromatograph equipped with a hydrogen flame detector and a 20% carbowax/firebrik column. Separate samples of the C copolymer were heated rapidly to 400, 600, and 800C. in the pyrolysis chamber. At 400C., only the C -alpha-olefm was detected. At 600C., about equal amounts of the olefin and lighter pyrolysis products were found, while at 800C., only complete pyrolysis products consisting of methane, ethylene, ethane, propylene, and propane were found.

DENSITY Density as a function of chain length was determined on the polymer series using a density gradient column. These data are shown in FIG. 2.

PERMEABILITY The gaseous permeability to oxygen and carbon dioxide of this series of polymers is quite high, with only the silicones and modified silicones showing high permeability. The relationship between alpha-olefin chain length and gaseous permeability (oxygen and carbon dioxide) for the C -C series is plotted in FIG. 3. Permeability was determined by a modified Linde volumetric cell on films from polymers having molecular weight in excess of 150,000 (M TENSILE MODULUS AND ELONGATION Samples of polymers from the same polymerization run as those submitted for permeability studies were used to determine the mechanical properties (tensile modulus, percent elongation, and ultimate elongation). These are presented in FIGS. 4 and 5.

Data were obtained in accordance with ASTM Method No. 1708 with a cross-head speed of 0.5 in./- min, the gauge length 0.90 in., a chart speed of 20 in./min, 74F, and a relative humidity of 53%.

RESULTS AND DISCUSSION It has been recognized that the olefin-S0 copolymers are not thermally stable and that thermal degradation occurs via an unzipping mechanism to yield mostly monomers. Mass-spectrometric thermal analysis indicates that the original comonomers are the only products of vacuum-pyrolytic degradation, and no other sulfur-containing products were found such as described by Naylor and Anderson; J. Amer. Chem. Soc., 76, 3962 (1954).

At higher temperatures under essentially flash pyrolysis conditions, the decomposition mechanism appears to be a chain-unzipping one to form the alpha-olefin and sulfur dioxide, followed by the pyrolysis of the alpha-olefin. An activation energy for degradation of approximately 46 kcal/mole is in line with a similar activation energy for pyrolysis of other chain-unzipping polymers such as polystyrene, variously reported from 55 to kcal/mole, and poly(methyl methacrylate), a good average being 40 kcal/mole. Initiation of degradation is in the C. range, and pyrolysis is generally complete at 225C. with a heating rate of 20C./min. It is noted that this value given for the activation energy is for the pyrolysis of the molten polymer, since the polymer melt temperatures for all of the polymers were well below their 175C. decomposition points. There is no real difference in the pyrolysis characteristics of the polymers as a function of chain length of the alpha-olefin comonomer. This is not unexpected since the ratedetermining step must involve an endgroup initiation or a chain scission of a carbon-sulfur linkage. The alphaolefin tail could be expected to play no great part in guiding the course of the pyrolytic reaction.

VARIATION OF PROPERTIES OF FUNCTION OF CHAIN LENGTH In the series studied, the polysulfones prepared from the commercial olefins range from a hard, brittle material prepared from the C -alpha-olefin to an elastomer obtained from the C -olefin. It can be seen from FIG. 5 that the permeabilities of oxygen and carbon dioxide reach a maximum at the C -based polymer. Also the tensile and elongation curves show a break at the C polymer. In addition, the minimum density is obtained with the C -based polymer as shown in FIG. 2. Our explanation for this behavior is that a plasticizing effect with the longer alpha-olefin chain is occurring since it can be shown that a C alpha-olefin can flexibilize a c -alpha-olefin-sulfone polymer. The plasticizing effect 5 should become more efficient as the chain length ot the alpha-olefin increases. However, we believe another effect occurs at C specifically, side chain crystallization. In this case the olefin side chain crystallizes inde- 6 tion, as described herein, utilizes a material not to our knowledge previously evaluated for blood oxygenation purposes and which shows better physical properties in the pure state than silicone rubber, and also compara- Pendently of the backbone of the p y thus lowef- 5 ble gas permeability and nonthrombogenic properties ing its mobility and its plasticizing action on the main relative to Silicone rubber chain Of the polymer. chain crystallization has For example to illustrate the biocompatibility n n d in s ra th m g s series of p ytowards blood, the classical Lee White clotting time mers. Overberger and co-workers, J. Amer. Chem. Soc., h d was d (R 1 L d p 1) whi A cli i. 3326 Studied a $6065 of p y(p y cal Study of the Coagulation Time of Blood, Am. J. styrenes) with the normal aliphatic groups (C -C Med. Sci. 145, 495 (1913). substituted in the para position. They found amaxi- The following average whole blood clotting times mum in tl'lE glass transition temperature OCCUl'lll'lg Wltl'l. (WBCT) were obtained for borosilicate glass and the the C side chain. If one adds the length of a four-car- C olefin-based polysulfone: bon unit for the approximate size of the para-phenylene TABLE II moiety, then the total chain length would be similar to a C carbon chain rather than a C chain: Surface Lee z g gy Time Glass, borosilicate 8.0 '7" Polysulfone coated pyrex glass 27.0

A typical literature WBCT value for silicone rubber is 27 minutes (Boretos, J. W., Pierce, W. S. Seg- 5 mented Polyurethane: A Polyether Polymer. An Initial Evaluation for Biomedical Applications. J. Biomed. Mater. Res. Vol. 2, p. 12, (1968).

The high biocompatibility of the polysulfones of this invention, as illustrated by the foregoing Lee White 30 test, indicates that this material will have utility for the fabrication of prosthetic devices in contact with body fluids, for example, heart valves, surgical implants, No direct evidence y data, was Obtained artificial arteries and veins, soft contact lenses, and for crystallinity in the polymers prepared. This does not drug delivery systems. rule out the proposed explanation for the variation in In addition the high biocompatibility coupled with properties as function of chain length, since small-size hi h permeability suggests their utility for surgical tape crystallites cannot always be recognized in a polymeric and wound dressings. matrix by x-ray analysis techniques. Purity of the mon- The inate flexibility and ease of forming, both by omer feed stock was ruled out as a factor for this variaolv nt sting and thermoplastic extrusion, coupled tion since a similar trend was found for polymers prewith the high biocompatibility suggests their use for pared from highly purified monomers. The permeation surgical tubing as for example in blood transfusion, data obtained from the ter-polymer systems (Table l) intravenous feedings, etc. also support this theory of competitive plasticization To indicate the utility of permeable membranes as versus side chain crystallization as a causative factor blood oxygenators, a man at rest consumes approxifor the maximum obtained for the physical properties. mately 18 liters per hour of oxygen. Therefore about TABLE I Permeability of Terpolymers Olefin O2 transmission CO2 transmission,

cc-millin -yr-atm cc-millin -yr-atm 90 Hexene-lO hexadecene 1,860 6,870 90 Hexene-lO hexadecene (plasticized) 4,340 Hexene-SO hexadecene 9,960 49,630 16.7 Hexene-83.3 hexadecene 33,070 110,250 3.3 Hexene-96.7 hexadecane 37,530 142,300 16.7 Hexadecene-83.3 octadecene 34,730 154,700 50 Hexadecene-SO octadecene 46,700 191,900

Figures before olefin indicate concentration in wt-%.

"Hexadecene, 10 wt%, used as a plasticizer for the hexane-sulfur dioxide copolymer.

Many membrance devices have been constructed of silicone rubber materials largely because of their high oxygen and carbon dioxide permeabilities and their reasonable non-thrombogenic properties. However, the poor mechanical properties of pure polysilicone materials require the use of high concentrations of silica filler which compromise their ultimate performance as a blood compatible biomaterial. This inven- Permselective membranes have also been used for:

instrumentation for gas analysis;

separation, purification and enrichment of gases;

preventing passage of micro-organisms in the pharmaceutical and fermentation industries. Also for surgical dressings; and breathing systems in general.

The physical properties of the copolymers areillustrated in FIGS. 1 through 5, FIG. 1 showing a plot of the alpha-olefin chain length (containing from C to C carbon atoms) against the melt temperature. FIG. 2 plots the alpha-olefin chain lengths from C to C carbon atoms against polymer density. FIG. 3 indicates the relationship between the olefin chain length and the O transmission rate as well as the CO transmission rate, each of the respective transmission rates being plotted against the alpha-olefin chain length from C to C carbon atoms. FIG. 4 plots the alpha-olefin chain length against tensile modulus and percent elongation. FIG. 5 plots the alpha-olefin chain length against the percent elongation at yield point.

The use of the alpha-olefin/SO copolymer is illustrated in FIG. 6 which shows a soft contact lens article 5 made from the readily processable copolymer of the alpha-olefin and S0 FIG. 7 shows the perfusion membrane 7 of the present invention made from the alphaolefin/S0 copolymer.

The membrane 7 is supported by a polyester backing and is used, for instance, in a membrane-lined, capillary oxygenator. As seen in FIG. 7, the membrane 7, made of the alpha-olefin/SO copolymer, is in contact with blood. The arrows show 0 entering the blood supply while CO leaves the blood through the membrane and the porous polyester backing which, in turn, is supported on porous substrate such as shown, for example, in the membrane-lined capillary oxygenator shown on page 139 of Transactions, American Society for Artificial Internal Organs, 1969.

The copolymers of alpha-olefin and S0 can be used in many of the biocompatible articles used in contact with body fluids such as artificial arteries, artificial veins, heart valves, surgical implants, blood storage bags and surgical tubing, illustrated in the above article, for example, on pages 170, 173, 179, 201, 212, 207, 246, 251, 256, 287 and 352.

FIG. 8 shows a biocompatible article 8 for contact with human body fluids made of a copolymer of an alpha-olefin and sulfur dioxide, the article being surgical tubing.

FIG. 9 illustrates a biocompatible article for contact with human body fluids, the article being an artificial heart 9, and an artificial vein 10 connected to the heart. As indicated previously, the biocompatible copolymer of alpha-olefin and sulfur dioxide can be used as an artificial heart valve, which is shown as valve 15 in FIG. 10. The valve 15 is toroidal in shape, and a perspective view of the toroidal valve 15 is shown in FIG. 11.

FIG. 12 illustrates another biocompatible article for use in contact with body fluids, the article being a wound dressing 20. The wound dressing 20 comprises a pair of porous polysulfone (copolymer of an alpha-olefin and S0 layers 22 and 23 with cotton between the two layers. As also shown in FIG. 12, the ends of the polysulfone layers are sealed to provide an excellent dressing.

As previously indicated, outstanding results have been obtained by the use of the alpha-olefin/SO copolymers described herein, including the new use of the biocompatible polymer comprising the steps of (1) making a biocompatible article for contact with human body fluids, the article being made of a copolymer of (a) an alpha-olefin having eight to eighteen carbon atoms and (b) sulfur dioxide, and (2) contacting human body fluids with the article of step I to provide a nonthrombogenic article having good oxygen and carbon dioxide permeabilities.

What is claimed is:

I. As an article of manufacture, a permselective, biocompatible membrane article having high gaseous permeability, said membrane consisting of a poly(alpha-olefin-sulfone) derived from the series C to C alpha-olefins and sulfur dioxide, the membrane having an oxygen transmission rate of about 1 to 4X10 cc mil./in yr atm. and a C0 transmission rate of about 4 to l7 l0 cc mil./in yr atm.

2. An article as defined in claim 1 wherein the radical contains fourteen carbon atoms and the alpha-olefin contains sixteen carbon atoms.

3. An article as defined in claim 1 in which the alphaolefin contains 14 carbon atoms.

4. An poly(alpha-olefin-sulfone) as defined in claim 1 in which the permeability to oxygen is measured by an O transmission rate of at least about 3.1 X 10 cc mil./in yr atm; the permeability to CO is at least about 13.9 X 10 cc mil./in yr atm; and the percent elongation at yield point is at least about 13.5.

5. A membrane article as defined in claim 1 that has an O transmission rate of about 3.75 X 10" cc mil./in yr atm; a C0 transmission rate of about 16.5 X 10 cc mil./in yr atm; and an elongation at yield point of about 14%. 

1. AS AN ARTICLE OF MANUFACTURE, A PERSELCTIVE, BIOCOMPATIBLE MEMBRANE ARTICLE HAVING HIGH GASEOUS PERMEABILITY, SAID MEMBRANE CONSISTING OF A POLY(ALPHA-OLEFIN-SULFONE) DERIVED FROM THE SERIES C8 TO C18 ALPHA-OLEFINS AND SULFUR DIOXIDE THE MEMBRANE HAVING AN OXYGEN TRANSMISSION RATE OF
 2. An article as defined in claim 1 wherein the radical contains fourteen carbon atoms and the alpha-olefin contains sixteen carbon atoms.
 3. An article as defined in claim 1 in which the alpha-olefin contains 14 carbon atoms.
 4. An poly(alpha-olefin-sulfone) as defined in claim 1 in which the permeability to oxygen is measured by an O2 transmission rate of at least about 3.1 X 10 4 cc mil./in2 yr atm; the permeability to CO2 is at least about 13.9 X 10 4 cc mil./in2 yr atm; and the percent elongation at yield point is at least about 13.5.
 5. A membrane article as defined in claim 1 that has an O2 transmission rate of about 3.75 X 10 4 cc mil./in2 yr atm; a CO2 transmission rate of about 16.5 X 10 4 cc mil./in2 yr atm; and an elongation at yield point of about 14%. 